1. Field of the Invention
The present invention relates to a semiconductor device, particularly to a semiconductor device having a capacitor.
2. Description of the Related Art
In recent years, development of a ferroelectric memory (FeRAM: Ferroelectric Random Access Memory) in which a ferroelectric film is used as a dielectric film of a capacitor has been advanced.
Examples of a typical ferroelectric film for use in the ferroelectric memory include a Pb(ZrxTi1-x)O3 film (PZT film) and SrBi2Ta2O9 film (SBT film). PZT is a perovskite compound, and SBT is a Bi aurivillius phase compound having a pseudo perovskite structure.
When the PZT film is used as the ferroelectric film, conductive perovskite metal oxide films such as an SrRuO3 film (SRO film) are used for an electrode from a viewpoint of improvement of a fatigue characteristic. For example, in Jpn. Pat. Appln. KOKAI Publication Nos. 2000-208725 and 2000-260954, a ferroelectric capacitor is described in which a stacked film of SRO and Pt films is used for the electrode.
On the other hand, in recent years, a ferroelectric memory having a capacitor-on-plug (COP) structure has been developed. Since a plug connected to a transistor is disposed right under the capacitor in the COP structure, it is possible to prepare a ferroelectric memory with a higher density. With the use of the COP structure, there is a fear of oxidation of the plug at a heat treatment under an oxygen atmosphere essential for preparing the ferroelectric capacitor. Therefore, it is necessary to use noble metal films, such as Ir film, which have good barrier properties, for the electrode.
Here, it is assumed that the stacked structure of SRO and Ir films is used for the electrode in the COP structure. In this case, Ir reacts with Sr included in the SRO film by the heat treatment, and a problem occurs that crystallinity of the SRO film remarkably drops. As a result, characteristics and reliability of the capacitor are remarkably deteriorated. This problem is generally caused in a combination of the conductive perovskite metal oxide film and noble metal film (or noble metal oxide film).
When the stacked structure of the conductive perovskite metal oxide film and noble metal film (or noble metal oxide film) is used for the electrode of the capacitor in this manner, there is a problem that the characteristics and reliability of the capacitor are remarkably deteriorated.